The present invention relates to a heat exchanger, and more particularly, to a heat exchanger having an improved header pipe and a manufacturing method of the header pipe.
Various types of heat exchangers such as a fin-tube type, a serpentine type and a parallel-flow type, are used depending on the characteristics of the heat exchange medium and the pressure in use. With freon gas used as the heat exchange medium being replaced by a heat exchange medium having an ozone depleting potential (ODP) of zero, the parallel-flow type heat exchanger is reputed to be most suitable due to its superior performance as well as small size and light weight.
FIG. 1 shows a general parallel-flow type heat exchanger. The heat exchanger 100 is comprised of a pair of header pipes 111 and 111' spaced by a predetermined distance and a plurality of flat tubes 112 which are disposed between the header pipes 111 and 111' to communicate therewith. The heat exchange medium flows through the header pipes 111 and 111' and the tubes 112. Fins 113 for enlarging the surface area for dissipating heat are formed between the tubes 112 and a cap 114 is provided at one end of each header pipe. The heat exchange medium is supplied via an inlet pipe 111a connected to the header pipes 111 and 111' and discharged via an outlet pipe 111a' after flowing through the header pipes 111 and 111' and the tubes 112. A baffle can be installed in the header pipes 111 and 111' to change the flow path of the heat exchange medium.
FIGS. 2A-2H schematically show a process of manufacturing a conventional header pipe for use in the heat exchanger 100 shown in FIG. 1, the process being disclosed in U.S. Pat. No. 4,945,635.
In the manufacturing process of the conventional header pipe, an aluminum sheet member, which is coated with an aluminum cladding layer thereon, is employed. An aluminum sheet member 221 as shown in FIG. 2A has the length corresponding to the length of a complete header pipe and the width being the same as or larger than the circumference of the sectional area of a completed header pipe, respectively. In FIG. 2B, slits 222 for receiving a baffle (not shown) are formed in the aluminum sheet member 221. The baffle is inserted into the header pipe through the slit 222 to change or limit the flow path of the heat exchange medium. The formation of the slits 222 and the use of the baffle are optional.
In FIG. 2C, the mid-section along the length of the sheet member 221 is rolled to form a semi-cylindrical portion member 221a, and as shown in FIG. 2D, a plurality of tube connecting apertures 223 into which the tubes 112 are inserted are formed at predetermined intervals in the semi-cylindrical portion member 221a. Next, a rolling process is performed to flat portions member 221b where the slits 222 are formed to form the sheet member 221 into a cylinder form. Here, a header pipe 225 is completed in the shape shown in FIG. 2F, via the shape shown in FIG. 2E. FIG. 2G is a view for explaining the flat tubes 226 having the fins 227 arranged therebetween are assembled into the tube connecting apertures 223 formed in the header pipe 225. The coupled header pipe 225 and the tubes 226 are completely coupled by brazing. FIG. 2H is a cross section showing a state where the tube and the header pipe are coupled by brazing.
There are some problems in the header pipe 225 having the above structure due to its shape. First, in the process of manufacturing the tube connecting aperture 223 in the header pipe 225 using a press, as shown in FIG. 2H, deformation occurs around a burred portion 223' of the tube connecting aperture 223, or the contact thickness (t') of the tube and the header pipe becomes less than the thickness (t) of the header pipe 225 since the tube connecting aperture 223 is formed on a curved surface and not on a plane, and as a result, the tube connecting aperture ends up being angled rather than vertical. Accordingly, the coupling of the burred portion of the tube 226 and the inner surface of the tube connecting aperture 223 of the header pipe 225 becomes unstable, and thus, though the brazing is performed, the junction therebetween is rendered incomplete to thereby cause leakage of the heat exchange medium. Also, an unnecessary space is formed around the tube 226 inserted into the inside of the header pipe 225 so that the flow efficiency of the heat exchange medium is lowered, the necessary amount of charge of the heat exchange medium is increased, and the size of the header pipe is increased. Thus, the miniaturization and lightness of the heat exchanger are hindered. Besides, it is difficult to adjust the depth to which the tube 226 is to be inserted into the header pipe 225 during manufacturing. Also, the area for brazing the tubes 226 to the header pipe 225 is limited only between the tubes and the apertures.
FIG. 3 shows a cross section of another conventional header pipe. The header pipe is manufactured by, first, rolling first and second sheet members 331 and 332 into a semi-cylindrical shape at a predetermined curvature and braze-coupling the sheet members 331 and 332. Both side edges of the first sheet member 331 are bent outward and again towards and overlaying the sheet member 332. The two sheet members are braze-coupled at positions indicated by reference numeral 334 between the inner surface of the bent portions 333 of the first sheet member 331 and the outer surface of both side edges of the second sheet member 332.
However, since the header pipe is constituted by separate members, a work process becomes complicated and the inside pressure of the header pipe is relatively lowered. Also, a complicated jig for joining the members is required when the members are put into a furnace for braze-coupling.